Datasheet DS1236S-5, DS1236S-10N, DS1236S-10, DS1236N-5, DS1236N-10 Datasheet (Dallas Semiconductor)

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FEATURES

 Holds microprocessor in check during power

transients

 Halts and restarts an out-of-control

microprocessor

 Monitors pushbutton for external override
 Warns microprocessor of an impending power

failure

 Converts CMOS SRAM into nonvolatile

memory

 Unconditionally write-protects memory when

power supply is out of tolerance

 Consumes less than 100 nA of battery current

at 25°C

 Controls external power switch for high

current applications

 Accurate 10% power supply monitoring
 Optional 5% power supply monitoring

designated DS1236-5

 Provides orderly shutdown in nonvolatile

microprocessor applications

 Supplies necessary control for low-power

“stop mode” in battery operated hand-held
applications

 Standard 16-pin DIP or space-saving 16-pin

SOIC

 Optional industrial temperature range -40°C

to +85°C

PIN ASSIGNMENT

PIN DESCRIPTION

V

BAT

- +3-Volt Battery Input

V

CCO

- Switched SRAM Supply Output
VCC - +5-Volt Power Supply Input
GND - Ground
PF - Power-Fail (Active High)

PF - Power-Fail (Active Low)

WC/

SC - Wake-Up Control (Sleep)

RC - Reset Control
IN - Early Warning Input

NMI - Non-Maskable Interrupt
ST - Strobe Input

CEO - Chip Enable Output
CEI - Chip Enable Input
PBRST - Pushbutton Reset Input
RST - Reset Output (Active Low)

RST - Reset Output (Active High)

DESCRIPTION

The DS1236 MicroManager Chip provides all the necessary functions for power supply monitoring, res et
control, and memory backup in microprocessor-based systems. A precise internal voltage reference and
comparator circuit monitor power supply status. When an out-of-tolerance condition occurs, the
microprocessor reset and power-fail outputs are forced active, and static RAM control unconditionally
write protects external memory. The DS1236 also provides early warning detection of a user-defined
threshold by driving a non-maskable interrupt. External reset control is provided by a pushbutton reset

DS1236

MicroManager Chip

www.dalsemi.com

16-Pin SOIC (300-mil)

See Mech. Drawings Section

VBAT

VCCO

VCC

RST
RST
PBRST

1
2
3

16
15
14

GND CEI413

PF
PF

WC/SC

CEO
ST
NMI

5
6
7

12
11
10

RCI IN

89

16-Pin DIP (300-mil)

See Mech. Drawings Section

VBAT

VCCO

VCC

RST
RST
PBRST

1
2
3

16
15
14

GND CEI413

PF
PF

WC/SC

CEO
ST
NMI

5
6
7

12
11
10

RC IN89

DS1236

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input which is debounced and activates reset outputs. An internal watchdog timer can also force the reset
outputs to the active state if the strobe input is not driven low prior to watchdog timeout. Reset control
and wake-up/sleep control inputs also provide the necessary signals for orderly shutdown and startup in
battery backup and battery operated applications. A block diagram of the DS1236 is shown in Figure 1.

PIN DESCRIPTION

PIN NAME DESCRIPTION

V

BAT

+3V battery input provides nonvolatile operation of control functions.

V

CCO

VCC output for nonvolatile SRAM applications.

V

CC

+5V primary power input.

PF Power-fail indicator, active high, used for external power switching as shown in

Figure 9.

PF

Power-fail indicator, active low.

WC/SC

Wake-up and Sleep control. Invokes low-power mode.

RC

Reset control input. Determines reset output. Normally low for NMOS processors and
high for battery backed CMOS processors.

IN Early warning power-fail input. This voltage sense point can be tied (via resistor

divider) to a user-selected voltage.

NMI

Non-maskable interrupt. Used in conjunction with the IN pin to indicate an impending
power failure.

ST

Strobe input. A high-to-low transition will reset the watchdog timer, indicating that
software is still in control.

CEO

Chip enable output. Used with nonvolatile SRAM applications.

CEI

Chip enable input.

PBRST

Pushbutton reset input.

RST

Active low reset output.

RST Active high reset output.

PROCESSOR MODE

A distinction is often made between CMOS and NMOS processor systems. In a CMOS system, power
consumption may be a concern, and nonvolatile operation is possible by battery backing both the SRAM
and the CMOS processor. All resources would be maintained in the absence of VCC. A power-down reset
is not issued since the low-power mode of most CMOS processors (Stop) is terminated with a Reset. A

pulsed interrupt (

NMI ) is issued to allow the CMOS processor to invoke a sleep mode to save power. For

this case, a power-on reset is desirable to wake up and initialize the processor. The CMOS mode is
invoked by connecting RC to V

CCO

.

An NMOS processor consumes more power, and consequently ma y not be battery backed. In this case, it
is desirable to notify the processor of a power-fail, then keep it in reset during the loss of VCC. This avoids
intermittent or aberrant operation. On power-up, the processor will continue to be reset until V

CC

reaches

an operational level to provide an orderly start. The NMOS mode is invoked by connecting RC to ground.

DS1236

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POWER MONITOR

The DS1236 employs a band gap voltage reference and a precision comparator to monitor the 5-volt
supply (VCC) in microprocessor-based systems. When an out-of-tolerance condition occurs, t he RST and

RST outputs are driven to the active state. The V

CC

trip point (V

CCTP

) is set for 10% operation so that the

RST and RST outputs will become active as VCC falls below 4.5 volts (4.37 typical). The V

CCTP

for the

5% operation option (DS1236-5) is set for 4.75 volts (4.62 typical). The RST and RST signals are
excellent for microprocessor reset control, as processing is stopped at the last possible moment of in-

tolerance V

CC

. On power-up, the RST and RST signals are held active for a minimum of 25 ms (100 ms

typical) after V

CCTP

is reached to allow the power supply and microprocessor to stabilize. Note: The
operation described above is obtained with the reset control pin (RC) connected to GND (NMOS mode).
Please review the reset control section for more information.

WATCHDOG TIMER

The DS1236 provides a watchdog timer function which forces the RST and RST signals to the active
state when the strobe input (ST ) is not stimulated for a predetermined time period. This time period is 400

ms typically with a maximum time-out of 600 ms. The watchdog time-out period be gins as soon as RST
and RST are inactive. If a high-to-low transition occurs at the ST input prior to time-out, the watchdog
timer is reset and begins to time out again. The ST input timing is shown in Figure 2. To guarantee the
watchdog timer does not time out, a high-to-low transition on ST must occur at or less than 100 ms
(minimum time-out) from a reset. If the watchdog timer is allowed to time out, the RST and RST outputs
are driven to the active state for 25 ms minimum. The ST input can be derived from microprocessor

address, data, and/or control signals. Under normal operating conditions, these signals would routinely
reset the watchdog timer prior to time-out. If the watchdog timer is not required, two methods have been
provided to disable it.

Permanently grounding the IN pin in the CMOS mode (RC=1) will disable the watchdog. In normal
operation with RC=1, the watchdog is disabled as soon as the IN pin is below VTP. With IN grounded, an

NMI output will occur only at power-up, or when the ST pin is strobed. As shown in the Figure 3, a

falling edge on ST will generate an NMI when IN is below VTP. This allows the processor to verify that
power is between VTP and V

CCTP

, as an NMI will be returned immediately after the ST strobe. The

watchdog timer is not affected by the IN pin when in NMOS mode (RC=0).

If the NMI signal is required to monitor supply voltages, the watchdog may also be disabled by leaving
the ST input open. Independent of the state of the RC pin, the watchdog is also disabled as soon as V

CC

falls to V

CCTP

.

PUSHBUTTON RESET

An input pin is provided on the DS1236 for direct connection to a pushbutton. The pushbutton reset input
requires an active low signal. Internally, this input is pulled high by a 10k resistor whenever VCC is

greater than V

BAT

. The PBRST pin is also debounced and timed such that the RST and RST outputs are
driven to the active state for 25 ms minimum. This 25 ms delay begins as the pushbutton is released from
a low level. A typical example of the power monitor, watchdog timer, and pushbutton reset connections
are shown in Figure 4. The PBRST input is disabled whenever the IN pin voltage level is less than V

TP

and the reset control (RC) is tied high (CMOS mode). The PBRST input is also disabled whenever VCC is
below V

BAT

. Timing of the PBRST -generated RST is illustrated in Figure 5.

DS1236

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NON-MASKABLE INTERRUPT

The DS1236 generates a non-maskable interrupt NMI for early warning of power failure to a
microprocessor. A precision comparator monitors the voltage level at the IN pin relative to a reference
generated by the internal band gap. The IN pin is a high-impedance input allowing for a user-defined
sense point. An external resistor voltage divider network (Figure 6) is used to interf ace with high voltage
signals. This sense point may be derived from the regulated 5-volt supply or from a higher DC voltage
level closer to the main system power input. Since the IN trip point VTP is 2.54 volts, the proper values
for R1 and R2 can be determined by the equation as shown in Figure 6. Proper operation of the DS1236
requires that the voltage at the IN pin be limited to VIN. Therefore, the maximum allowable voltage at the
supply being monitored (V

MAX

) can also be derived as shown in Figure 6. A simple approach to solving
this equation is to select a value for R2 high enough to keep power consumption low, and solve for R1.
The flexibility of the IN input pin allows for detection of power loss at the earliest point in a power

supply system, maximizing the amount of time for microprocessor shutdown between

NMI and RST or

RST .

When the supply being monitored decays to the voltage sense point, the DS1236 pulses the NMI output
to the active state for a minimum of 200 µs. The NMI power-fail detection circuitry also has built-in time

domain hysteresis. That is, the monitored supply is sampled periodically at a rate determined by an
internal ring oscillator running at approximately 30 kHz (33 µs/cycle). Three consecutive samplings of
out-of-tolerance supply (below V

SENSE

) must occur at the IN pin to a ctivate NMI . Therefore, the supply

must be below the voltage sense point for approximately 100 µs o r the comparator will reset. In this way,
power supply noise is removed from the monitoring function, preventing false trips. During a power-up,

any IN pin levels below VTP are disabled from reaching the NMI pin until VCC rises to V

CCTP

. As a result,

any potential NMI pulse will not be initiated until VCC reaches V

CCTP

.

Removal of an active low level on the NMI pin is controlled by either an internal time-out (when IN pin
is less than VTP) or by the subsequent rise of the IN pin above VTP. The initiation and removal of the NMI
signal during power-up results in an NMI pulse of from 0 µs minimum to 500 µs maximum, depending

on the relative voltage relationship between VCC and the IN pin voltage. As an example, when the IN pin
is tied to ground during power-up, the internal time-out will result in a pulse of 200 µs minimum to 500
µs maximum. In contrast, if the IN pin is tied to V

CCO

during power-up, NMI will not produce a pulse on

power-up. Note that a fast slewing power supply may cause the

NMI to be virtually nonexistent on

power-up. This is of no consequence, however, since an RST will be active.

DS1236

5 of 19

DS1236 FUNCTIONAL BLOCK DIAGRAM Figure 1

If the IN pin is connected to V

CCO

, the NMI output will pulse low as VCC decays to V

CCTP

in the NMOS

mode (RC=0). In the CMOS mode (RC=V

CCO

) the power-down of VCC out-of-tolerance at V

CCTP

will not
produce a pulse on the NMI pin. Given that an y NMI pulse has been completed by the time VCC decays
to V

CCTP

, the NMI pin will remain high. The NMI voltage will follow VCC down until VCC decays to

V

BAT

. Once VCC decays to V

BAT

, the NMI pin will either remain at V

OHL

or enter tri-state mode as

determined by the RC pin (see “Reset Control” section).

MEMORY BACKUP

The DS1236 provides all of the necessary functions required to battery back a static RAM. First, a switch
is provided to direct SRAM power from the incoming 5-volt supply (V

CC

) or from an external battery

(V

BAT

), whichever is greater. This switched supply (V

CCO

) can also be used to battery back a CMOS
microprocessor. For more information about nonvolatile processor applications, review the “Reset
Control” and “Wake Control” sections. Second, the same power-fail detection described in the power

monitor section is used to hold the chip enable output (

CEO ) to within 0.3 volts of V

CC

or to within 0.7

volts of V

BAT

. This write protection mechanism occurs as VCC falls below V

CCTP

as specified. If CEI is

DS1236

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low at the time power-fail detection occurs, CEO is held in its present state until CEI is returned high, or
the period tCE expires. This delay of write protection until the current memory cycle is completed prevents

the corruption of data. If CEO is in an inactive state at the time of VCC fail detection, CEO will be
unconditionally disabled within tCF. During nominal supply conditions CEO will follow CEI with a

maximum propagation delay of 20 ns. Figure 7 shows a typical nonvolatile SRAM application.

FRESHNESS SEAL

In order to conserve battery capacity during storage and/or shipment of an end system, the DS1236
provides a freshness seal to electrically disconnect the battery. Figure 8 depicts the three pulses below
ground on the IN pin required to invoke the freshness seal. The freshness seal will be disconnected and
normal operation will begin when VCC is cycled and reapplied to a level above V

BAT

.

To prevent negative pulses associated with noise from setting the freshness mode in system applications,
a series diode and resistor can be used to shunt noise to ground. During manuf acturing, the freshness seal
can still be set by holding TP2 at -3 volts while applying the 0 to –3 volts clock to TP1.

POWER SWITCHING

When larger operating currents are required in a battery backed system, the 5-volt supply and battery
supply switches internal to the DS1236 may not be large enough to support the required load through

V

CCO

with a reasonable voltage drop. For these applications, the PF and PF outputs are provided to gate
external power switching devices. As shown in Figure 9, power to the load is switched from VCC to
battery on power-down, and from battery to VCC on power-up. The DS1336 is designed to use the PF
output to switch between V

BAT

and VCC. It provides better leakage and switchover performance than
currently available discrete components. The transition threshold for PF and PF is set to the external
battery voltage V

BAT

, allowing a smooth transition between sources. The load applied to the PF pin from
the external switch will be supplied by the battery. Therefore, if a discrete switch is used, this load should
be taken into consideration when sizing the battery.

RESET CONTROL

As mentioned above, the DS1236 supports two modes of operation. The CMOS mode is used when the
system incorporates a CMOS microprocessor which is battery backed. The NMOS mode is used wh en a
non-battery backed processor is incorporated. The mode is selected b y the RC (Reset Control) pin. The

level of this pin distinguishes timing and level control on RST,

RST , and NMI outputs for volatile

processor operation versus nonvolatile battery backup or battery operated processor applications.

ST/INPUT TIMING Figure 2

DS1236

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NMI/FROM ST/INPUT Figure 3

POWER MONITOR, WATCHDOG Figure 4

PUSH BUTTON RESET TIMING Figure 5

NON-MASKABLE INTERRUPT Figure 6

DS1236

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EXAMPLE 1: 5 VOLT SUPPLY, R2 = 10k OHM, V

SENSE

= 4.80 VOLTS

∴∴∴∴ 4.80 =

10k

10

k

R1+

X 2.54 R1 = 8.9k OHM

EXAMPLE 2: 12 VOLT SUPPLY, R2 = 10k OHM, V

SENSE

= 9.00 VOLTS

∴∴∴∴ 9.00 =

10k

10

k

R1+

X 2.54 R1 = 25.4k OHM

V

MAX

=

2.54

9.00

X 5.00 = 17.7 VOLTS

NONVOLATILE SRAM Figure 7

DS1236

9 of 19

When the RC pin is tied to ground, the DS1236 is designed to interface with NMOS processors which do
not have the microamp currents required during a battery backed mode. Grounding the RC pin does,
however, continue to support nonvolatile backup of system SRAM memory. Nonvolatile systems
incorporating NMOS processors generally require that only the SRAM memory and/or timekeeping
functions be battery backed. When the processor is not battery backed (RC = 0), all signals connected
from the processor to the DS1236 are disconnected from the backup battery suppl y, or grounded when
system V

CC

decays below V

BAT

. In the NMOS processor system, the principal emphasis is placed on

giving early warnings with

NMI , then providing a continuously active RST and RST signal during

power-down while isolating the backup battery from the processor during a loss of VCC.
During power-down, NMI will pulse low for a minimum of 200 µs, and then return high. If RC is tied

low (NMOS mode), the voltage on NMI will follow VCC until VCC supply decays to V

BAT

, at which point

NMI will enter tri-state (see timing diagram). Also, upon V

CC

out-of-tolerance at V

CCTP

, the RST and

RST outputs are driven active and RST will follow V

CC

as the supply decays. On power-up, RST follows

VCC up, RST is held low, and both remain active for t

RST

after valid VCC. During a power-up from a V

CC

voltage below V

BAT

, any detected IN pin levels below VTP are disabled from reachin g the NMI pin until

VCC rises to V

CCTP

. As a result, any potential NMI pulse will not be initiated until VCC reaches V

CCTP

.

Removal of an active low level on the NMI pin is controlled by either an internal time-out (when the IN
pin is less than VTP), or by the subsequent rise of the IN pin above VTP. The initiation and removal of the

NMI signal results in an NMI pulse of 0 µs minimum to 500 µs maximum during power-up, depending

on the relative voltage relationship between VCC and the IN pin. As an example, when the IN pin is tied to
ground, the internal timeout will result in a pulse of 200 µs minimum to 500 µs maximum. In contrast, if
the IN pin is tied to V

CCO

, NMI will not produce a pulse on power-up.

Connecting the RC pin to a high (V

CCO

) invokes CMOS mode and provides nonvolatile support to both
the system SRAM as well as a low power CMOS processor. When using CMOS microprocessors, it is
possible to place the microprocessor into a very low-power mode termed the “st op” or “halt” mode. In
this state the CMOS processor requires only microamp currents and is fully capable of being battery
backed. This mode generally allows the CMOS microprocessor to maintain the contents of internal RAM
as well as state control of I/O ports during battery backup. The processor can subsequently be restarted by

any of several different signals. To maintain this low-power state, the DS1236 issues no NMI and/or reset
signals to the processor until it is time to bring the processor back into full operation. To support the low-

power processor battery backed mode (RC = 1), the DS1236 provides a pulsed

NMI for early power

failure warning. Waiting to initiate a Stop mode until after the NMI pin has returned high will guarantee
the processor that no other active NMI or RST/ RST will be issued by the DS1236 until one of two

conditions occurs: 1) Voltage on the pin rises above V

TP

, which activates the watchdog, or 2) VCC cycles

below then above V

BAT

, which also results in an active RST and RST . If VCC does not fall below V

CCTP

,

the processor will be restarted by the reset derived from the watchdog timer as the IN pin rises above VTP.

With the RC pin tied to V

CCO

, RST and RST are not forced activ e as VCC collapses to V

CCTP

. The RST is

held at a high level via the ex t ernal batt ery as V

CC

falls below battery potential. This mode of operation is

intended for applications in which the processor is made nonvolatile with an external source, and allows
the processor to power down into a Stop mode as signaled from NMI at an earlier voltage level. The NMI

output pin will pulse low for t

NMI

following a low voltage detect at the IN pin of VTP. Following t

NMI

,

however, NMI will also be held at a high level (V

BAT

) by the battery as VCC decays below V

BAT

. On

power-up, RST and RST are held inactive until VCC reaches V

BAT

, then RST and RST are driven active

for t

RST

. If the IN pin falls below VTP during an active reset, the reset outputs will be forced inactive by

the NMI output. In addition, as long as the IN pin is less than VTP, stimulation of the ST pin will result in

DS1236

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additional NMI pulses. In this way, the ST pin can be used to allow the CMOS processor to determine if
the supply voltage, as monitored by the IN pin, is above or below a selected operating value. This is
illustrated in Figure 3. As discussed above, the RC pin determines the timing relationships and levels of
several signals. The following section describes the power-up and power-down timing diagrams in more
detail.

TIMING DIAGRAMS

This section provides a description of the timing diagrams shown in Figure 10, Figure 11, Figure 12, and
Figure 13. These diagrams show the relative timing and levels in both the NMOS and the CMOS mode
for power-up and down. Figure 10 illustrates the relationship for power-down in CMOS mode. As V

CC

falls, the IN pin voltage drops below VTP. As a result, the processor is notified of an impending power
failure via an active NMI , which allows it to enter a sleep mode. As the power falls further, VCC crosses
V

CCTP

, the power monitor trip point. Since the DS1236 is in CMOS mode, no reset is generated. The RST

voltage will follow VCC down, but will fall no further than V

BAT

. At this time, CEO is brought hi gh to

write protect the RAM. When the VCC reaches V

BAT

, a power-fail is issued via the PF and PF pins.

Figure 11 illustrates operation of the power-down sequence in NMOS mode. Once again, as power falls,
an NMI is issued. This gives the processor time to save critical data in nonvolatile SRAM. When V

CC

reaches V

CCTP

, an active RST and RST are given. The RST voltage will follow VCC as it falls. CEO , PF,

and PF will operate in a similar manner to CMOS mode. Notice that the NMI will tri-state to prevent a
loss of battery power.

Figure 12 shows the power-up sequence for the NMOS mode. As VCC slews above V

BAT

, the PF and PF

pins are deactivated. An active reset occurs as well as an NMI . Although the NMI may be short due to
slew rates, reset will be maintained for the standard t

RST

timeout period. At a later time, if the IN pin falls
below VTP, a new NMI will occur. If the processor does not issue a ST , a watchdog reset will also occur.
The second NMI and RST are provided to illustrate these possibilities.

Figure 13 illustrates the power-up timing for CMOS mode. The principal difference is that the DS1236
issues a reset immediately in the NMOS mode. In CMOS mode, a reset is issued when IN rises above

VTP. Depending on the processor type, the NMI may terminate the Stop mode in the processor.

WAKE CONTROL/SLEEP CONTROL

The Wake/Sleep Control input (WC/ SC ) allows the processor to disable all comparators on the DS1236
before entering the Stop mode. This feature allows the DS1236, processor, and static RAM to maintain
nonvolatility in the lowest power mode possible. The processor may invoke the sleep mode in battery
operated applications to conserve batter y capacity when an absence of activit y is detected. The operatio n
of this signal is shown in Figure 14. The DS1236 may subsequently be restarted by a high-to-low

transition on the PBRST input through human interface via a keyboard, touchpad, etc. The processor will
then be restarted as the watchdog times out and drives RST and

RST active. The DS1236 can also be

started up by forcing the WC/SC pin high from an external source. Also, if the DS1236 is placed in a
sleep mode by the processor and system power is lost, the DS1236 will wake up the next time V

CC

rises

above V

BAT

. These possibilities are illustrated in Figure 15.

When the sleep mode is invoked during normal power-valid conditions, all operation on the DS1236 is
disabled, thus leaving the

NMI , RST, and RST outputs disabled as well as the ST and IN inputs.

However, a loss of power during a sleep mode will result in an active RST and RST when the RC pin i s
grounded (NMOS mode). If the RC pin is tied high, the RST and RST pins will remain inactive during

DS1236

11 of 19

power-down in a sleep mode. Removal of the sleep mode by the PBRST input is not affected by the IN
pin threshold at VTP when the RC pin is tied high (CMOS mode). Subsequent power-up of the VCC supply

with the RC pin tied high will activate the RST and RST outputs as the main supply rises above V

BAT

. A

high-to-low transition on the WC/ SC pin must follow a high-to-low transition on the ST pin by tWC to
invoke a Sleep mode for the DS1236.

FRESHNESS SEAL Figure 8

NOTE: This series of pulses must be applied during normal +5 volt operation.

POWER SWITCHING Figure 9

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CMOS MODE POWER-DOWN (RC = V

CCO

) Figure 10

DS1236

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NMOS MODE POWER-DOWN (RC = GND) Figure 11

DS1236

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NMOS MODE POWER-UP (RC = GND) Figure 12

DS1236

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CMOS MODE POWER-UP (RC = V

CCO

) Figure 13

DS1236

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WAKE/SLEEP CONTROL Figure 14

OPTIONS FOR INVOKING WAKEUP Figure 15

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ABSOLUTE MAXIMUM RATINGS*

Voltage on VCC Pin Relative to Ground -0.5V to +7.0V
Voltage on I/O Relative to Ground -0.5V to VCC + 0.5V
Voltage on IN Pin Relative to Ground -3.5V to VCC + 0.5V
Operating Temperature 0°C to 70°C
Operating Temperature (Industrial Version) -40°C to +85°C
Storage Temperature -55°C to +125°C
Soldering Temperature 260°C for 10 seconds

* This is a stress rating only and functional operation of the device at these or any other conditions

above those indicated in the operation sections of this specification is not implied. Exposure to
absolute maximum rating conditions for extended periods of time may affect reliability.

RECOMMENDED DC OPERATING CONDITIONS (0°C to 70°C)

PARAMETER SYMBOL MIN TYP MAX UNITS NOTES

Supply Voltage V

CC

4.5 5.0 5.5 V 1

Supply Voltage (5% Option) V

CC

4.75 5.0 5.5 V 1

Input High Level V

IH

2.0 VCC+0.3 V 1

Input Low Level V

IL

-0.3 +0.8 V 1

IN Input Pin V

IN

-0.3 VCC+0.3 V 1

Battery Input V

BAT

2.7 4.0 V 1

DC ELECTRICAL CHARACTERISTICS (0°C to 70°C; VCC= 4.5V to 5.5V)

PARAMETER SYMBOL MIN TYP MAX UNITS NOTES

Supply Current I

CC

4mA2

Sleep Supply Current in Sleep
mode

I

CC

20

µA

Battery Current I

BAT

0.1

µA

2

Supply Output Current
(V

CCO=VCC

- 0.3V)

I

CC01

100 mA 3

Supply Output Current in Data
Retention (VCC < V

BAT

)

I

CC02

1mA4

Supply Output Voltage V

CCO

VCC-0.3 V 1

Battery Backup Voltage V

CCO

V

BAT

-0.7 V 1, 6

Low Level @ RST V

OL

0.4 V 1

Output Voltage @ -500 µA

V

OH

VCC-0.5V VCC-0.1V V 1

CEO and PF Output

V

OHL

V

BAT

-0.7 V 1, 6

PBRST Pull-up Resist

R

PBRST

10k Ohms

Input Leakage Current I

LI

-1.0 +1.0

µA

18

Output Leakage Current I

LO

-1.0 +1.0

µA

18

Output Current @ 0.4V I

OL

4.0 mA 12

DS1236

18 of 19

PARAMETER SYMBOL MIN TYP MAX UNITS NOTES

Output Current @ 2.4V I

OH

-1.0 mA 13

Power Sup. Trip Point V

CCTP

4.25 4.37 4.50 V 1

Power Supply Trip (5% Option) V

CCTP

4.50 4.62 4.75 V 1

IN Input Pin Current I

CCIN

-1.0 +1.0

µA

IN Input Trip Point V

TP

2.5 2.54 2.6 V 1

AC ELECTRICAL CHARACTERISTICS (0°C to 70°C; VCC= 4.5V to 5.5V)

PARAMETER SYMBOL MIN TYP MAX UNITS NOTES

VCC Fail Detect to RST, RST

t

RPD

40 100 175

µs

VTP to NMI

t

IPD

40 100 175

µs

RESET Active Time t

RST

25 100 150 ms

NMI Pulse Width

t

NMI

200 300 500

µs

14

ST Pulse Width

t

ST

20 ns 19

PBRST @ V

IL

t

PB

30 ms

VCC Slew Rate 4.75 to 4.25 t

F

300

µs

Chip Enable Propagation Delay t

PD

20 ns

VCC Fail to Chip Enable High t

CF

71244

µs

17

VCC Valid to RST, RST (RC=1)

t

FPU

100 ns

VCC Valid to RST & RST

t

RPU

25 100 150 ms 5

VCC Slew to 4.24 to V

BAT

t

FB1

10

µs

7

VCC Slew 4.25 to 4.75 V

BAT

t

FB2

100

µs

8

Chip Enable Output Recovery
Time

t

REC

.1

µs

9

VCC Slew 4.25 to 4.75 t

R

0

µs

Chip Enable Pulse Width t

CE

5s10

Watchdog Time Delay t

TD

100 400 600 ms

ST to WC/SC

t

WC

0.1 50

µs

V

BAT

Detect to PF, PF

t

PPF

2

µs

7

ST to NMI

t

STN

30 ns 11

NMI to RST & RST

t

NRT

30 ns

V

BAT

Detect to RST & RST

t

ARST

200

µs

15

VCC Valid to RST, RST

t

BRST

30 100 150

µs

16

DS1236

19 of 19

CAPACITANCE (tA=25°C)

PARAMETER SYMBOL MIN TYP MAX UNITS NOTES

Input Capacitance C

IN

5pF

Output Capacitance C

OUT

7pF

NOTES:

1. All voltages referenced to ground. A 0.1 µF capacitor is recommended between VCC and GND.

2. Measured with V

CCO

, CEO , PF, ST , PBRST , RST, RST , and NMI pin open. I

BAT

specified at 25°C.

3. I

CCO1

is the maximum average load which the DS1236 can supply at VCC-0.3V through the V

CCO

pin

during normal 5-volt operation.

4. I

CCO2

is the maximum average load which the DS1236 can supply through the V

CCO

pin during data

retention battery supply operation, with a maximum drop of 0.8 volts.

5. With tR = 5 µs.

6. V

CCO

is approximately V

BAT

-0.5V at 1 µA load.

7. Sleep mode is not invoked.

8. Sleep mode is invoked.

9. t

REC

is the minimum time required before CEI / CEO memory access is allowed.

10. tCE maximum must be met to ensure data integrity on power loss.

11. IN input is less than VTP but VCC greater than V

CCTP

.

12. All outputs except RST which is 25 µA maximum.

13. All outputs except RST and NMI which is 25 µA minimum.

14. Pulse width of NMI requires that the IN pin remain below VTP. If the IN pin returns to a level above

VTP for a period longer than t

IPD

and before the t

NMI

period has elapsed, the NMI pin will immediately

return to a high.

15. IN pin greater than V

TP

when VCC supply rises to V

BAT

. Example: IN tied to GND.

16. IN pin less than VTP when VCC supply rises to V

BAT

.

17. CEI low.

18. The WC/

SC pin contains an internal latch which drives back on to the pin. This latch requires ±200

µamps to switch states. The ST pin will sink ±50 µamps in normal operation and ±1 µamp in the
sleep mode.

19.

ST should be active low before the watchdog is disabled (i.e., before the ST input is tristated).